As the frequency of operation of radar antennas increases, the spacing between the radiating elements that make up the aperture becomes smaller. For example, the spacing may be less than 1.0 cm (0.400″) center-to-center at 16 GHz (Ku band). In addition, effective phased array radars can have 10,000 or more radiating elements. The radiating elements in these assemblies have critical alignment requirements. They also require isolation between adjacent radiating elements and excellent grounding.
Previous processes formed the mechanical attachment between adjacent radiating elements in a phased array aperture with epoxy joints and machined features in soft-substrates such as “Duroid®”. Materials such as polytetrafluoroethylene (PTFE) and “Duroid®” (PTFE/glass or PTFE/ceramic composites) exhibit poor dimensional stability, cold flow characteristics, and deformation under cutting stresses. Unlike metals, features machined in these materials cannot be relied upon to provide the positional alignment required in a high/wide band phased array aperture. Therefore to achieve element-to-element alignment and orientation, radiating elements were assembled using complicated tooling that required tedious fabrication procedures.
For example, a “rake” tool and a joe block were used to position and align individual radiating elements in an array, with each element on a respective substrate. The rake was used to establish a predetermined spacing between cells in the array, and the individual substrates were then positioned around the joe block to establish the correct orientation and location of the substrates. The array was built up by adding individual radiating elements. In the case of stripline circuit elements assembled in this manner, plated through-holes (vias) were used for isolation between adjacent radiating elements. This type of assembly can also have spurious grounds due to uneven or decaying epoxy joints.
An improved array structure and method of making the array is desired.